The vaso-active effects of inositol nicotinate (Hexopal) were investigated in thirty patients with primary and secondary Raynaud's phenomenon using several non-invasive experimental techniques under controlled conditions. The earlier formed impression that this drug requires a prolonged 'build-up' period was confirmed. Recording the time required to induce Raynaud's phenomenon as well as assessments of total and nutrient digital blood flow showed significant beneficial therapeutic effects upon the skin's microcirculation by inositol nicotinate. This study suggests that the therapeutic effect of this drug is not merely due to vasodilation but that other mechanisms such as enhanced fibrinolysis and lowering of serum lipids may play a significant part in its overall effect. Smokers responded slower than non-smokers, but even elderly patients with longstanding vasospastic disease showed measurably improved digital circulation. Unlike some other drugs in this field inositol nicotinate was found to be effective orally and to be devoid of unwanted side-effects. However, in the majority of patients it failed to abolish their increased vascular spasm although it diminished it significantly in most. It appears to be a safe and well tolerated drug, which, together with other symptomatic measures, merits to be used in the management of vasospastic disease of the extremities even in the presence of partial obliteration of the microcirculation.